Hydraulic control valve



United States Patent 3,081,787 HYDRAULIC CONTROL VALVE John W. Meuiendyk, Kalamazoo, Mich., assignor to Pneumo Dynamics Corporation, Cleveland, Ohio, a corporation of Delaware Filed July 13, 1961, Ser. No. 123,725 13 Claims. (Cl. 137--83) The instant invention relates to hydraulic control valves of the servo type having a two stage operation in which, the first stage comprises control elements for controlling operation of the second stage, and the latter operating to control the flow of hydraulic fluid to a hydraulic power mechanism which is operated by the hydraulic fluid.

it is an object of the instant invention to provide a novel hydraulic control valve of the servo type in which a relatively small quantity of hydraulic fluid is utilized to control the flow of substantially larger quantities of hydraulic fluid to a hydraulic power mechanism, which is operated by the relatively larger quantities of hydraulic fluid.

It is a further object of this invention to provide a novel hydraulic control valve in which control is achieved in response to a control signal supplied to the control valve.

It is also an object of the instant invention to provide a novel hydraulic control valve comprising electric motor control means adapted to be supplied with an electric control signal, with the controlled operation of the hydraulic elements of the valve being in response to the control signal supplied to the motor.

it is still another object of the instant invention to provide a novel hydraulic control valve in which there is provided a control jet of hydraulic fluid under pressure which controls the positioning of a second stage control element in response to a control signal supplied to the valve.

Still a further object of the instant invention is to provide a novel hydraulic control valve in which there is a torque motor adapted to be operated by a control signal supplied to the torque motor, for control of a jet of hydraulic fluid under pressure by which hydraulic control is achieved.

Further objects and advantages of the instant invention will be apparent to those skilled in the art from the following detailed description thereof which follows, reference being had to the drawing wherein:

The drawing is a diagrammatic illustration of a hydraulic control valve constructed in accordance with the instant invention.

The hydraulic control valve of this invention includes a valve housing in the upper part of which there is a torque motor 11 by which operation of the hydraulic control elements is initiated; The torque motor 11 has an upper pair of permanent magnets 12, 13 and a lower pair of permanent magnets 14, 15, with the permanent magnets of each pair being disposed on opposite sides of an upright armature 16, and being of opposite polarity. The armature 16 is supported on a torque rod 17 which extends laterally with respect to the armature 16, and has its opposite ends fixedly secured in the valve housing 10. In the absence of a control signal to the torque motor 11, the torque rod 17 maintains the armature 16 in null position, equidistantly disposed with respect to poles of the permanent magnets 12, 13, 14, 15. Windings 18, 19 on the armature 16 are connected in a suitable manner to an electrical signal producing system, which supplies an electrical control signal to the windings 18, 19, and by which there is established a magnetic flux for rotating the armature 16 about the axis of the torque rod 17. The direction of rotation of armature 16 is in accordance with the direction of the electrical signal input to the windings 18 19, and the length of the are through which the armature 16 is rotated will be directly proportional to the magnitude of the electrical control signal supplied to the windings 18, 19. The torque rod 17 operates in the system to provide a mechanical spring force which resists rotation of the armature 16, and when the electrical control signal is cut otf from the windings 18, 19, the torque rod 17 acts to return the armature 16 to its null position.

The lower part of the valve housing Ill has a first pressure port 20 at one side of the valve housing 10, and a second pressure port 21 at the opposite side of the valve housing 10. Hydraulic fluid under pressure is supplied to each of the pressure ports 20, 21. A return port 22 for return of hydraulic fluid is disposed at a position intermediate the pressure ports 20, 21. A first controlled port 23 is disposed adjacent the first pressure port 20, and a second controlled port 24 is disposed adjacent the second pressure port 21, and as will be described in greater detail hereinafter, the controlled port 23 is adapted to receive hydraulic fluid under pressure from the pressure port 20, and the controlled port 24 is adapted to receive hydraulic fluid under pressure from the pressure port 21.

The valve housing 10 is formed with a first cylindrical chamber 25 at one side thereof, and a second cylindrical chamber 26 at the other side thereof, said cylindrical chambers 25, 26 being axially aligned. with each other. A valve spool 27, having a substantially cylindrical con figuration, is reciprocably supported in the opposite cylindrical chambers 25, 26, and the contacting portions of the valve spool 27 and the cylindrical chambers 25, 26 are in sealing engagement with each other to prevent leakage of hydraulic fluid. As illustrated in the drawing, the valve spool 27 is disposed in its null position, in which there is no flow of hydraulic fluid from either of the pressure ports 20, 21 to the controlled ports 23, 24, respectively.

The valve spool 27 is formed with an annular channel 30, which is aligned with the first pressure port 20 in the null position of the valve spool 27, and is in cornmunication with the first pressure port 20 in all positions of the valve spool 27. An internal flow passage 31 is formed in the valve spool 27 and connects to the annular channel 30, whereby a stream of hydraulic fluid under pressure is led through the flow passage 31. The flow passage 31 leads the hydraulic fluid under pressure to a discharge orifice 32 formed at the end of flow passage 31. The discharge orifice 32 is upwardly directed to discharge a supply jet of hydraulic fluid under pressure from the flow passage 31.

A hydraulic fluid transfer tube 33 is provided at the lower end of the torque motor armature 16. The transfer tube 33 may be formed in an enlarged body member 34 which is integral with the torque motor armature 16, or the transfer tube 33 may be formed as a separate element which is secured or connected to the armature 16. In any event, operating movement of the torque motor armature 16, as above described, also operates to move the transfer tube 33 about the axis of the torque rod 17.

The transfer tube 33 is formed with an inlet 35 for the reception of hydraulic fluid under pressure from the discharge orifice 32. and the inlet 35 is spaced from the discharge orifice 32 a sufficient distance to clear the valve spool 27 in all operated positions of the transfer tube 33. The inlet 35 is substantially larger in diameter than the discharge orifice 32, so that the supply jet of hydraulic fluid under pressure, which is discharged from the discharge orifice 32, will be received by the transfer tube inlet 35 in all operated positions of the transfer tube 33. The transfer tube 33 extends from the inlet 35 in an arcuate path and terminates in a transfer tube discharge orifice 36, which is adapted to discharge a control jet of hydraulic fluid under pressure from the transfer tube 33.

The valve spool 27 has a first receiver 37 and a second receiver 38, both of which are adapted to receive the hydraulic fluid under pressure which is discharged in a control jet from the transfer tube discharge orifice 36. The first receiver 37 is formed with a receiving orifice 40 and the second receiver 38 is formed with a receiving orifice 41. The receiving orifices 40, 41 are closely disposed to each other and are equidistantly spaced from the transfer tube discharge orifice 36 in the null position of the elements, as illustrated in the drawing. The transfer tube discharge orifice 36 is spaced from the valve spool 27 a suflicient distance to clear the valve spool 27 in all operated positions of the transfer tube 33.

In the null position of the elements, as shown in the drawing, the control jet of hydraulic fluid under pressure will be discharged from the transfer tube discharge orifice 36 into the receiving orifices 40, 41, and thence into the receivers 37, 38, respectively. Since the receiving orifices 40, 41 are'equidistantly spaced from the transfer tube discharge orifice 36, the hydraulic fluid under pressure of the control jet will be equally divided between the receivers 37, 38. A flow passage 42 leads hydraulic fluid under pressure from the receiver 37 through the valve spool 27 in an axial direction to the firs-t cylindrical chamber 25, in which the hydraulic fluid under pressure acts on the first end face 43 of the valve spool 27. A second flow passage 44 leads hydraulic fluid under pressure from the receiver 38 through the valve spool 27 in an axial direction to the second cylindrical chamber 26, in which the hydraulic fluid under pressure acts on the second end face 45 of the valve spool 27. In the null position of the elements, as illustrated in the drawing, the quantity of flow of hydraulic fluid under pressure to the receivers 37, 38 and thence to the cylindrical chambers 25, 26, respectively, is equal, and equal forces act on the opposite end faces 43, 45 of the valve spool 27, whereby the valve spool 27 is maintained stationary in its null position. In this condition of the elements there is, of course, no control signal being supplied to the torque motor 11, whereby the torque motor armature 16 is also maintained in null position.

The discharge orifice 32 and the receiving orifices 40, 41 are aligned with each other along a line that is parallel to the axis of the valve spool 27. The transfer tube inlet 35 and the transfer tube discharge orifice 36 are disposed on a line which is also parallel to the axis of the valve spool 27. Thus, there is defined a plane of alignment, which includes the line passing through the centers of the transfer tube inlet 35 and the transfer tube discharge orifice 36, the line passing through the centers of the discharge orifice 32 and the receiving orifices 40, 41, and the axis of valve spool 27. This plane of alignment is maintained by :1 lug 46 which is fixedly secured in the valve housing and is mated with an elongated slot 47 in the valve spool 27, to prevent rotation of the valve spool 27.

Movement of the valve spool 27 in one direction or the other is accomplished by supplying an appropriate electrical control signal to the torque motor 11. Thus, when an electrical control signal is supplied to the torque motor 11, the windings 18, 19 are energized creating a magnetic flux. Assuming that the direction of the electrical control signal is such as to rotate the torque motor armature 16 in a counterclockwise direction, the transfer tube 33 will be moved in the same direction, and the transfer tube discharge orifice 36 will be moved to the right so that it will be disposed out of equal registry with the receiving orifices 40, 41. When the transfer tube discharge orifice 36 is moved to the right as aforesaid, the control jet of hydraulic fluid under pressure will supply a greater quantity of hydraulic fluid to the receiver 37 than is reccivcd by the receiver 38, as a result of which there will be a greater force acting on the first end face43 of the valve spool 27 than the force acting on the second end face 45 of the valve spool 27. This unbalance of forces acting on the end faces 43, 45 of the valve spool 27 will cause the latter to move to the right, as viewed in the drawing, until the receiving orifices 40, 41 are again disposed in equal registry with the transfer tube discharge orifice 36, which will again produce equal division of the control jet of hydraulic fluid under pressure to the receivers 37, 38, with a balance of the hydraulic forces acting on the valve spool end faces 43, 45, which will maintain the valve spool 27 in its adjusted position. The magnitude of the electrical control signal delivered to the windings 18, 19 in the torque motor 11 will determine the amount of movement of the torque motor armature 16 and the transfer tube 33. If there is produced a greater movement of transfer tube 33, it will require a greater movement of the valve spool 27 to bring the receiving orifices 40, 41 back to equal registry with the transfer tube discharge orifice 36, whereby the travel of the valve spool 27 will be directly proportional to the magnitude of the electrical signal input to the torque motor 11, and the direction of movement of the valve spool 27 will also be in accordance with the direction of the input signal to the torque motor 11. When the electrical signal to the torque motor 11 is cut off, the torque rod 17 will return the torque motor armature 16 to its null position, whereby the transfer tube 33 will also experience a return move ment to null position. There is thus again created an unbalance of hydraulic forces acting on the opposite end faces 43, 45 of the valve spool 27 which will produce movement of the valve spool 27 in the opposite direction to return it to its null position, in which the hydraulic forces acting on the end faces 43, 45 will again be in bal ance to maintain valve spool 27 stationary.

When the valve spool 27 is moved to the right, as viewed in the drawing, the first pressure port 20 is connected by the annular channel 30 to the controlled port 23, for flow of hydraulic fluid under pressure through the controlled port 23. The hydraulic fluid under pressure may be delivered from the controlled port 23 through a line 50 to a cylinder and piston mechanism 51 for operation of the latter by the hydraulic fluid under pressure. A line 52 from the cylinder and piston mechanism 51 returns hydraulic fluid to the controlled port 24. When the valve spool 27 is moved to the right, the annular channel 53 connects the controlled port 24 to the return port 22, from which the hydraulic fluid may be returned to a reservoir, or the like. When the valve spool 27 is moved to the left, an annular channel 54 connects the second pressure port 21 to the controlled port 24, for delivery of hydraulic fluid under pressure through the line 52 to the cylinder and piston mechanism 51 for operating the latter. The line 50 then serves as a return line for return of hydraulic fluid to the controlled port 23. An annular channel 55 connects the controlled port 23 to the return port 22, by which the hydraulic fluid is returned to a reservoir, or the like. The cylinder and piston mechanism 51 which is illustrated in the drawings is merely representative of hydraulic power mechanisms which can be operated by the hydraulic control valve of this invention.

The hydraulic control valve of this invention comprises two stages of operation in the first of which the transfer tube 33 is controlled by the torque motor 11, and in the second stage of operation the valve spool 27 is controlled by the control jet of hydraulic fluid under pressure produced by the transfer tube 33. 'In this hydraulic control valve, relatively small electric control currents are utilized to control the flow of relatively large quantities of hydraulic fluid. In order to achieve this result, the first stage of the control valve, which produces the control jet of hydraulic fluid under pressure operates with relatively small quantities of hydraulic fluid, the flow of which is controlled by the torque motor which is operated by the relatively small electrical control currents. The second stage of the hydraulic control valve, comprising the valve spool 27, is operated by the relatively small control jet produced by the first stage, and the valve spool 27 in turn controls the flow of the substantially larger quantities of hydraulic fluid which are required for operation of the hydraulic power mechanism. By this invention there is provided a novel two stage hydraulic control valve of the servo type.

Obviously those skilled in the art may make various changes in the details and arrangements of parts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and it is therefore desired that the invention not be restricted to the precise construction herein disclosed Having thus described and shown an embodiment of the invention, what it is dfiired to secure by Letters Patent of the United States is:

l. A valve comprising a spool having a null position, a source of fluid under pressure, means in said spool for receiving fluid under pressure from said source, flow directing means for receiving fluid under pressure from said means in said spool, a first receiver and a second receiver for said fluid, said flow directing means including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

2. A valve comprising a spool having a null position, a source of fluid under pressure, passage means in said spool communicable with said source of fluid under pressure a flow transfer tube for receiving fluid under pressure from said means in said spool, a first receiver and a second receiver for said fluid, said transfer tube including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means connected to said transfer tube for displacing the transfer tube for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced transfer tube to maintain the spool in said second position.

3. A valve comprising a spool having a null position, a source of fluid under pressure including means disposed in said spool for delivering a jet of fluid under pressure, flow directing means including an inlet for receiving said jet of fluid under pressure from said means disposed in said spool in all positions of the flow directing means, a first receiver and a second receiver for said fluid, said fluid directing means including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

4. A valve comprising a spool having a null position, a source of fluid under pressure including means disposed in said spool to deliver said lluid under pressure in a supply jet, llow directing means including an inlet for receiving said supply jet of fluid under pressure from said means disposed in said spool in all positions of the flow directing means, a first receiver and a second receiver for said fluid, said flow directing means including a discharge for directing a control jet of fluid under pressure into said first and second receivers in equal flow quantities, means for applying fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing said control jet of fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

5. A valve comprising a spool having a null position, a passage in said spool for fluid under pressure, said passage including an orifice for delivering said fluid under pressure in a supply jet, flow directing means disposed adjacent said discharge orifice for receiving said supply jet of fluid under pressure, a first receiver and a second re ceiver for said fluid, said flow directing means including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

6. A valve comprising a spool having a null position, a passage in said spool for fluid under pressure, said passage including a discharge orifice for delivering said fluid under pressure in a supply jet, flow directing means including an inlet spaced from said discharge orifice for receiving said supply jet of fluid under pressure, a first receiver and a second receiver for said fluid, said flow directing means including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

7. A valve comprising a spool having a null position, a passage in said spool for fluid under pressure, said passage having a discharge orifice for delivering said fluid under pressure in a supply jet, flow directing means including an inlet which is substantially larger than said discharge orifice for receiving said supply jet of fiuid under pressure in all positions of the flow directing means, a first receiver and a second receiver for said fluid, said flow directing means including a discharge orifice for directing a control jet of fluid under pressure into said first and second receivers in equal flow quantities, means for applying the lluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, means for displacing said flow directing means for directing said control jet of fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position to a second position in which equal fiow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

8. A valve comprising a spool having a null position, a source of fluid under pressure, a passage in said spool communicable with said source, a transfer tube for receiving fluid under pressure from said passage in said spool, a first receiver and a second receiver for said fluid, said transfer tube including a discharge for directing fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, a torque motor including an armature adapted to be displaced by a control signal supplied to the torque motor, said transfer tube being connected to the armature for displacement of the transfer tube by the armature for directing fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position in accordance with the control signal to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced flow directing means to maintain the spool in said second position.

9. A valve comprising a spool having a null position, a passage in the spool for fluid under pressure, a discharge orifice for delivery from said passage of said fluid under pressure in a supply jet, a transfer tube having an inlet spaced from said discharge orifice, said inlet being substantially larger than the discharge orifice for receiving said supply jet of fluid under pressure in all positions of the transfer tube, a first receiver and a second receiver for said fluid, said transfer tube including a discharge orifice spaced from said first and second receivers to direct a control jet of fluid under pressure into said first and second receivers in equal flow quantities, means for applying the fluid under pressure from said first and second receivers to oppositely disposed portions of the spool to maintain the spool in null position, a torque motor having an armature adapted to be displaced in response to a control signal supplied to the torque motor, said transfer tube being connected to the armature for displacement of the transfer tube by the armature to direct said jet of fluid under pressure into said first and second receivers in unequal flow quantities to displace the spool from its null position in accordance with the control signal to the torque motor to a second position in which equal flow quantities of fluid under pressure are delivered to said first and second receivers from the displaced transfer tube to maintain the spool in said second position.

10. A valve comprising a spool having a null position, an inlet port for supply of fluid under pressure to the valve, a flow passage in the spool for leading a stream of fluid pressure from said inlet port to a discharge opening, a first receiver and a second receiver for fluid under pressure, flow directing means receiving fluid under pressure from said discharge opening and directing the flow thereof to said first and second receivers, said first and second receivers being disposed in registry with said flow directing means in the null position of the spool for equal division of the fluid under pressure to the first and second receivers, means for leading the divided streams of fluid under pressure from the first and second receivers to oppositely disposed portions of the spool to apply equal and opposite force to the spool to maintain the spool in null position, means for displacing said flow directing means with respect to said first and second receivers for unequal division of flow of the fluid under pressure to the first and second receivers for application of unequal forces to said oppositely disposed portions of the spool to displace the spool from null position, said first and second receivers being returned to registry with the flow directing means by displacement of the spool for equal division of the fluid under pressure to the first and second receivers to maintain the spool in displaced position.

11. A valve comprising a spool having a null position, an inlet port for supply of fluid under pressure to the valve, a flow passage in the spool for leading a stream of fluid under pressure from said inlet port to a discharge orifice for delivering said fluid under pressure in a supply jet, :1 first receiver and a second receiver for fluid under pressure, flow directing means including an inlet for receiving said supply jet of fluid under pressure from the discharge orifice in all positions of said flow directing means and directing fluid under pressure to said first and second receivers, said first and second receivers being disposed in registry with said flow directing means in the null position of the spool for equal division of the fluid under pressure to the first and second receivers, means for leading the divided fluid under pressure from the first and second receivers to oppositely disposed portions of the spool to apply equal and opposite force to the spool to maintain the spool in null position, means for displacing said flow directing means with respect to said first and second receivers for unequal division of fluid under pressure to the first and second receivers for application of unequal forces to said oppositely disposed portions of the spool to displace the spool from said null position, said first and second receivers being returned to registry with the flow directing means by displacement of the spool for equal division of the fluid under pressure to the first and second receivers to maintain the spool in displaced position.

12. A valve comprising a spool having a null position, an inlet port for supply of fluid under pressure to the valve, a flow passage in the spool for leading a stream of fluid under pressure from said inlet port to a discharge orifice for delivery of fluid under pressure in a supply jet, a first receiver and a second receiver for fluid under pressure, a transfer tube having an inlet which is substantially larger than said discharge orifice for receiving the supply jet of fluid under pressure from the discharge orifice in all positions of the transfer tube, said transfer tube including a discharge orifice for directing said fluid under pressure in a control jet to said first and second receivers, said first and second receivers being disposed in registry with said transfer tube discharge orifice in the null position of the spool for equal division of the fluid under pressure to the first and second receivers, means for leading the fluid under pressure from the first and second receivers to oppositely disposed portions of the spool to apply equal and opposite force to the spool to maintain the spool in null position,

means for displacing said transfer tube with respect to said first and second receivers for unequal division of the fluid under pressure to the first and second receivers for application of unequal forces to said oppositely disposed portions of the spool to displace the spool from null position, and said first and second receivers being returned to registry with the transfer tube discharge orifice by displacement of the spool for equal division of the fluid under pressure to the first and second receivers to maintain the spool in displaced position.

13. A valve comprising a spool having a null position, an inlet port for supply of fluid under pressure to the valve, a flow passage in the spool for leading a stream of fluid under pressure from said inlet port to a discharge orifice for delivering fluid under pressure in a supply jet, a first receiver and a second receiver for fluid under pressure, a transfer tube having an inlet for receiving said supply jet of fluid under pressure from the discharge orifice, said inlet being substantially larger than said discuarge orifice for receiving the supply jet of fluid under pressure in all positions of the transfer tube, said transfer tube including a discharge orifice for directing a control jet of fluid under pressure to said first and second receivers, said first and second receivers being disposed in registry with the transfer tube discharge orifice in the null position of the spool for equal division of the jet of fluid under pressure to the first and second receivers, means for leading the divided fluid under pressure from the first and second receivers to oppositely disposed portions of the spool to apply equal and opposite force to the spool to maintain the spool in null position, a torque motor having an armature adapted to be displaced in accordance with control signal supplied to the torque motor, said transfer tube being connected to the armature for displacement of the transfer tube by the armature to displace the transfer tube discharge orifice with respect to said first and second receivers for unequal division of flow of the fiuid under pressure to the first and second receivers for application of unequal forces to said oppositely disposed portions of the spool to displace the spool from null position, and said first and second receivers being returned to registry with the transfer tube discharge orifice by displacement of the spool for equal division of the fluid under pressure to the first and second receivers to maintain the spool in dis placed position.

References Cited in the file of this patent UNITED STATES PATENTS 2,047,922 Seligmann July 14, 1936 2,742,022 Jacques Apr. 17, 1956 10 2,884,907 Atchley May 5, 1959 2,997,064 Gerwig et al Aug. 22, 1961 

1. A VALVE COMPRISING A SPOOL HAVING A NULL POSITION, A SOURCE OF FLUID UNDER PRESSURE, MEANS IN SAID SPOOL FOR RECEIVING FLUID UNDER PRESSURE FROM SAID SOURCE, FLOW DIRECTING MEANS FOR RECEIVING FLUID UNDER PRESSURE FROM SAID MEANS IN SAID SPOOL, A FIRST RECEIVER AND A SECOND RECEIVER FOR SAID FLUID, SAID FLOW DIRECTING MEANS INCLUDING A DISCHARGE FOR DIRECTING FLUID UNDER PRESSURE INTO SAID FIRST AND SECOND RECEIVERS IN EQUAL FLOW QUANTITIES, MEANS FOR APPLYING THE FLUID UNDER PRESSURE FROM SAID FIRST AND SECOND RECEIVERS TO OPPOSITELY DISPOSED PORTIONS OF THE SPOOL TO MAINTAIN THE SPOOL IN NULL POSITION, MEANS FOR DISPLACING SAID FLOW DIRECTING MEANS FOR DIRECTING FLUID UNDER PRESSURE INTO SAID FIRST AND SECOND RECEIVERS IN UNEQUAL FLOW QUANTITIES TO DISPLACE THE SPOOL FROM ITS NULL POSITION TO A SECOND POSITION IN WHICH EQUAL FLOW QUANTITIES OF FLUID UNDER PRESSURE ARE DELIVERED TO SAID FIRST AND SECOND RECEIVERS FROM THE DISPLACED FLOW DIRECTING MEANS TO MAINTAIN THE SPOOL IN SAID SECOND POSITION. 